Captain Slow

Hi all. It's storming here today, so I'm flinging wrenches in the attic, finally getting around to
re-roadworthy-ing a '94 Trek 1220 that was given to me (wrecked) ten years ago.

Catch was, I got it sans wheels. The bike has Shimano RX100 stuff, triple front, 7-speed rear.
Except for the wheel-less situation, it's in good nick, looks to be barely used. I suspect that
the first owner had it racked on his car trunk and backed into something... crushing both
wheels.

I have several spare wheelsets, all OEM equipment from 9-speed bikes. Just playing today, I
fit a 7-speed cassette onto one of those rear wheels, and shimmed it with spacers from old
cassettes until the cogs were snug against the lockring.

Looks like it ought to work, at least it indexes properly... Hopefully the chain won't find its
way past the 25t and fall between it and the spokes... That'd be a bad thing. I may have to
look around here for one of those plastic spoke protector discs that I remove at first
opportunity.

Anyway, I have a couple of questions for the mix-n-match riders/readers/posters out there:

1) Any of you run a 7-speed cassette on a 9-speed rear wheel?

B) Am I right in shimming the cogs toward the axle end ? (spacers at the back) Any problems
I might expect?

III) Anybody run a 9-speed chain on a 7-speed gruppo? Any gotchas with that?
(I have a big box of CN-HG73 chains on hand, thanx to e-bay & Mastercard.)

Thanks in advance.

joejack951

Given that newer hubs got wider and to do so the width was added to the outside, to be more "correct", you'd want to add the spacers on the outside thus keeping the cassette where it was originally intended to be located. With that said, what really matters is your chainline. If it's fine with the spacers on the inside, and you like it better that way, just leave it.

The only downside might be an increased throw required to shift with the front derailler due to the narrower chain in the wide derailler cage, and possibly an increased chance of jamming the chain in between the crank arms and outer chainring. To address the former, you could always swap the FD for a 9 speed version. For the latter, just make sure your stops are set proplerly.

Retro Grouch 

No. I don't think that's right.

Your derailleur is mounted on the dropout and it indexes from the drive side locknut. The chainline is designed for that orientation too. That's why mountain bikes use a 5mm longer bottom bracket spindle.
Spacers installed behind your cassette won't be a problem.

joejack951

You make a good point that I hadn't thought of but you can easily adjust the inner and outer stops on a derailler. Without a new bottom bracket, you can't change the position of your chainrings. Of course, this is assuming that the derailler has sufficient inward adjustment.

Sekine

And if it doesn't, try finding a longer screw (just don't force anything, breakage is bad).

9sp chain on a 7sp cassette might also lead to sticking of the chain, the cogs are slightly wider as well and (are your chainrings designed for 9 or 7?) sometimes the chain sticks to either the cogs or chainrings getting pulled around further than it should then popping off. If that happens, get a wider chain, if it doesn't, sweet.

anti.team

I use a 9sp chain on a 7sp cassette and have not had a single issue with the chain. In general, you can use a chain designed for more speeds than your cassette. The chain is not any narrower internally, only externally. You should be just fine with 9sp chain.

Bill Kapaun

You need a 4.5MM spacer (about $2 at the LBS) to use the 7 speed cassette on an 8/9 FH body, as you probably know.
Does your shifter have a friction mode? IF so, and you have time on your hands (and a caliper), you might make it an 8 speed, using the 7 speed cogs?
I did this by sanding down the 7 speed spacers to about .110" or maybe a bit less.
I used a sheet of 200 grit emery cloth taped down. 20 strokes, rotate 1/3 turn repeat, measure in 3 places. When you start to get close, temporarily assemble to see how much further you need to go to seat the lock ring.
It took me about 45 minutes, once I got serious and determined how much pressure I could use.
Don't try a belt sander! DOES NOT WORK WELL!
You'll find that the spacers have "ridges" on each side. Those sand down quickly.
I was able to keep all my spacers within .002-3" and even without much trouble.
I now have a custom cassette to match my needs.
13-14-15-16-17-19-21-24 with the option of throwing a 12, 18, 23, 26 or 28T cog into the mix.
Just Saying....

DannoXYZ 

Or you can just buy the 8-spd spacers for converting 7 to 8-spd. I've done the sanding/grinding down part and it takes some time for the precision needed. Measure regulary with some calipers at 4-points around the spacer.

Also, you do want to keep the 4.5mm spacer behind the cogs. You really want the smallest 1st cog to be about 5mm away from the dropout so that the indexing works the same. That way, you can swap in other 7-spd wheels and not have to re-adjust the derailleur. I will actually juggle axle-spacers to the left side to place the smallest-cog about 3.5-4.0mm away from the dropout. This reduces wheel-dish and creates a stronger rear-wheel due to more balanced spoke-tensions between the left & right sides.

Captain Slow

My thanks to all for the tips & suggestions.

I'll get a 4.5mm spacer from the shop... The stack of old cassette inner spacers that I kluged yesterday works okay, but isn't up to my usual standard.

I test rode the rig this morning at zero-dark-thirty (and who doesn't enjoy making repairs in the dark?) and was amazed to have had almost no problems. Couple of times when moving to an easier RD cog, I had to shift twice... past my target cog, then back down to it... but that's just a fine tuning issue. Otherwise, RD indexes as I'd expect it to, and the friction FD does its retro thing as advertised.

Right now, I'm using a 7-speed chain. I had one left from years ago. I preferred these fatter outside-measurement chains... I remember getting upwards of 3,500 - 4,000 miles out of 'em, unlike the new
narrower chains. If I end up using the 1220 a lot, I'll probably buy a couple of spares, and leave the
9-speed chains for my other bikes.

Sadly, this makes five roadworthy bikes in my stable. I may have to take early retirement from my job so I'll have time to ride them all.